Microsoft’s Security Essentials (MSE) is the US's most popular antivirus program in a stubbornly fragmented market, new figures from OPSWAT have found.

Using figures collected during 2011 from the company’s AppRemover utility run on 170,000 PCs, MSE was the most popular antivirus program in the US with a near 15 percent share, or nearly 10 percent globally where it was just behind the world number one, Avast Free, on 11.9 percent.

Judged by global vendor share, Microsoft grew from just over 6 percent in the 2010 survey (which used a smaller data set) to just over 10 percent in 2011. In the US, where Symantec is still the biggest vendor with a 16 percent share, Microsoft is now number two on 14.9 percent.

OPSWAT found that the top 10 detected vendors now account for 87.5 percent of the global antivirus market, a list also dominated by companies that are either free or offer a free version.

All the expected names are on this list, but four of the top five – Avast, Avira, AVG, and ESET – are now companies based on the ‘freemium’ model in which consumers only pay for premium versions of each vendor’s antivirus programs. The other, Microsoft, is entirely free.

Brand-wide, Avast still leads the market with 16.2 percent (a figure that includes paid versions), a slightly reduced share from 2010, with the next four battling it out in a range between 10 and 11.6 percent.

The top 'traditional' vendor is still Symantec, which has held its share steady at just under 10 percent, ahead of Kaspersky (7.7 percent), McAfee (4.7 percent), Panda (3.7 percent), and Trend Micro (2.2 percent).

Beyond the popularity of MSE and free or freemium antivirus generally, the market remains relatively fragmented, especially in the US.

In few technology markets would as many as 10 vendors be so close on market share, which suggests that the complexity of PC security and the need for constant innovation makes it hard for a few vendors to shut out smaller rivals completely.

Despite a lineage that stretches back to an acquired company called Sybari, MSE’s existence as a totally free antivirus product began with the release of version 1.0 in 2009. This was followed a year later by 2.0, which added a network intrusion detection element.

Microsoft is currently testing a third incarnation among its developer network.